The mystery of the missing snow
The Colorado River watershed is an ideal site to study sublimation, as the phenomenon occurs more often in dry climates. In recent years, there have also been unexplainable decreases in the river’s flow, which people in seven states depend upon for drinking water. In 2021, the Colorado River snowpack was estimated at 80% of average, but streamflows ended up being only 30% of average. The researchers speculate that the discrepancy may in part be explained by sublimation.
“Forty million people depend on the Colorado River, and snow is the biggest input in the water resource equation,” Hogan says. “We don’t really know how much water is being lost from sublimation definitively.”
Current models used to predict sublimation rely on a fundamental theory, developed in flat cornfields in Kansas in the 1950s, that has proven to be inaccurate in more complex terrain, such as mountainous regions. Models based on this theory vary widely in terms of how much snow is predicted to sublimate, ranging from 10-90%.
“A simple way to explain why the theory in the prairie doesn’t apply in complex terrain is to imagine a river flow — it behaves well over smooth ground, but if you introduce bumps to the river bed, the flow becomes complicated,” Schwat says.
To improve future models, the researchers are working to better understand the precise combination of conditions that lead to sublimation, which tends to occur during low temperatures, low humidity and when both strong sunlight and wind are present. Since sublimation impacts snow on the surface and likely the snowflakes blowing above, the researchers will be paying close attention to the top layer of snow. They’ll also be investigating the characteristics of the turbulent air motions above — which can fluctuate widely depending on wind and other conditions.
“Studies show that when snowflakes are picked up by the wind and blown around, they may sublimate, so blowing snow is not necessarily just deposited elsewhere,” Schwat explains.
